U.S. patent application number 12/644627 was filed with the patent office on 2010-04-22 for belt-type continuous stepless speed changer.
This patent application is currently assigned to YAMAHA HATSUDOKI KABUSHIKI KAISHA. Invention is credited to Yousuke ISHIDA, Masaru OOSUGA.
Application Number | 20100099524 12/644627 |
Document ID | / |
Family ID | 32929669 |
Filed Date | 2010-04-22 |
United States Patent
Application |
20100099524 |
Kind Code |
A1 |
ISHIDA; Yousuke ; et
al. |
April 22, 2010 |
BELT-TYPE CONTINUOUS STEPLESS SPEED CHANGER
Abstract
A belt-type continuously variable transmission includes a
primary sheave including a pair of first clamp surfaces, a
secondary sheave including a pair of second clamp surfaces, and a
belt endlessly wound between both of the primary and secondary
sheaves. The belt includes contact surfaces clamped between the
first clamp surfaces and between the second clamp surfaces. Powder
having infusibility as a friction enhancing material is held on at
least one of the first clamp surfaces of the primary sheave, the
second clamp surfaces of the secondary sheave, and the contact
surfaces of the belt.
Inventors: |
ISHIDA; Yousuke; (Shizuoka,
JP) ; OOSUGA; Masaru; (Shizuoka, JP) |
Correspondence
Address: |
YAMAHA;C/O KEATING & BENNETT, LLP
1800 Alexander Bell Drive, SUITE 200
Reston
VA
20191
US
|
Assignee: |
YAMAHA HATSUDOKI KABUSHIKI
KAISHA
Iwata-shi
JP
|
Family ID: |
32929669 |
Appl. No.: |
12/644627 |
Filed: |
December 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10547614 |
May 15, 2006 |
7648435 |
|
|
PCT/JP2004/001972 |
Feb 20, 2004 |
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12644627 |
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Current U.S.
Class: |
474/8 |
Current CPC
Class: |
F16G 5/166 20130101;
F16H 9/18 20130101; F16H 55/56 20130101; F16H 55/38 20130101 |
Class at
Publication: |
474/8 |
International
Class: |
F16H 55/56 20060101
F16H055/56 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2003 |
JP |
2003-054219 |
Oct 29, 2003 |
JP |
2003-369016 |
Claims
1. A sheave for a continuously variable transmission, comprising: a
pair of clamp surfaces arranged to clamp a belt; and friction
layers including infusible powder disposed on the pair of clamp
surfaces.
2. A sheave for a continuously variable transmission according to
claim 1, wherein the pair of clamp surfaces include a plurality of
recesses arranged to hold the powder.
3. A sheave for a continuously variable transmission according to
claim 1, wherein the friction layers include a material made of a
mixture of a binder and carbon black powder.
4. A sheave for a continuously variable transmission according to
claim 1, wherein the powder has such a characteristic that, when
the belt is clamped between the pair of clamp surfaces, the powder
is not fused by heat that is generated by friction between the belt
and the pair of clamp surfaces.
5. A sheave for a continuously variable transmission according to
claim 1, wherein the powder has a hardness that is less than that
of the pair of clamp surfaces.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a belt-type continuously
variable transmission that transmits a torque of a primary sheave
to a secondary sheave via an endless belt, and a sheave and a belt
that are used in this continuously variable transmission, and more
particularly to a structure for preventing slipping of the belt at
an initial stage of driving. Further, the present invention relates
to a vehicle such as a motorcycle mounted with the belt-type
continuously variable transmission.
[0003] 2. Description of the Related Art
[0004] JP-A-2002-147553, for instance, discloses a belt-type
continuously variable transmission for motorcycles, which can
steplessly adjust a transmission gear ratio according to a
condition of running. This belt-type continuously variable
transmission includes a primary sheave, a secondary sheave, and a
belt.
[0005] The primary sheave is driven by power transmission from an
engine. The primary sheave has a pair of clamp surfaces opposed to
each other and a belt groove formed between these clamp surfaces.
The secondary sheave is interlocked with a rear wheel of the
motorcycle via a reduction mechanism. This secondary sheave has a
pair of clamp surfaces opposed to each other and a belt groove
formed between these clamp surfaces.
[0006] The belt is endlessly wound between the belt groove of the
primary sheave and the belt groove of the secondary sheave. The
belt has contact surfaces for contact with the clamp surfaces of
the respective sheaves. Torque of the primary sheave is transmitted
to the secondary sheave via the belt by frictional force generated
between the contact surfaces of the belt and the clamp surfaces of
the respective sheaves.
[0007] As is shown in FIG. 18, this kind of belt-type continuously
variable transmission has a characteristic that, as thrust, which
causes the clamp surfaces of the respective sheaves to clamp the
belt, increases, the torque transmissible between the sheaves and
the belt increases accordingly. When the thrust acting on the belt
increases, a great frictional resistance is generated between the
clamp surfaces of the sheaves and the contact surfaces of the belt,
and an amount of heat generation of the belt increases. The heat
generation of the belt indicates that kinetic energy is converted
into thermal energy. The transmission efficiency of torque
decreases by a degree corresponding to the conversion from kinetic
energy to thermal energy.
[0008] FIG. 19 shows transition of an amount of heat generation of
the belt and transmission efficiency at the time when the thrust
acting on the belt is varied. As it is evident from FIG. 19, if the
thrust increases, the amount of heat generation of the belt
increases in proportion to the increase in the thrust, and the
transmission efficiency of torque decreases. Therefore, it is
necessary to set the thrust to a necessary minimum level in order
to increase the transmission efficiency of torque between the
sheaves and the belt.
[0009] On the other hand, in the belt-type continuously variable
transmission, the clamp surfaces of the respective sheaves are
subjected to machining such as cutting and grinding. This kind of
machining is performed while the sheave is being rotated.
Therefore, a large number of annular grooves along a peripheral
direction are formed on the clamp surfaces of the sheaves. The
grooves are very fine with width and depth of about several
.mu.m.
[0010] Incidentally, according to the conventional belt-type
continuously variable transmission, when driving is started in a
newly assembled state, slipping tends to occur in the belt, in
particular, at the initial stage of driving. FIG. 20 shows
transition of transmission torque of the belt at the initial stage
of driving. As it is evident from FIG. 20, the torque transmitted
to the belt is significantly lower than a predetermined set value C
immediately after driving is started. A value of this torque tends
to gradually increase as driving time elapses. After certain time
elapses, the torque reaches the set value.
[0011] It is assumed that this phenomenon occurs because of the
grooves present on the clamp surfaces of the sheaves in a brand new
state. In short, it appears that the presence of the grooves makes
a contact state between the sheaves and the belt unstable, causing
the slip of the belt.
[0012] Therefore, in driving the new belt-type continuously
variable transmission, trial-runs of the continuously variable
transmission need to be performed until the torque transmitted to
the belt reaches the set value. By performing the trial-runs, the
contact surfaces of the belt are abraded by edges of the grooves of
the sheaves and sharp edges of the grooves are worn. Consequently,
the grooves of the sheave are filled with abrasion waste and the
clamp surfaces of the sheaves are smoothed. As a result, the state
of contact between the sheaves and the belt is stabilized and the
slip of the belt is controlled. As shown in FIG. 20, desired
transmission torque is obtained when predetermined trial-run is
completed.
[0013] In the conventional belt-type continuously variable
transmission, however, the trial-runs need to be continued until
the slip of the belt is completely eliminated. Consequently, long
time is required until the continuously variable transmission is
set in a drivable state and a great deal of labor is required for
shipment of the product, causing an increase in cost.
[0014] In order to control the slipping of the belt at the initial
stage of driving, it is conceivable to increase the thrust acting
on the belt. However, if the thrust is increased, the amount of
heat generation of the belt inevitably increases as described
above. Therefore, after the completion of the trial-run, the thrust
acting on the belt becomes excessively large and the transmission
efficiency of the torque is deteriorated.
SUMMARY OF THE INVENTION
[0015] Preferred embodiments of the present invention provide a
belt-type continuously variable transmission that prevents slipping
of a belt while controlling thrust acting on the belt to a
necessary minimum necessary level, and a vehicle including such a
belt-type continuously variable transmission.
[0016] According to a preferred embodiment of the present
invention, a sheave for a continuously variable transmission
includes a pair of clamp surfaces arranged to clamp a belt, and
friction layers including infusible powder disposed on the pair of
clamp surfaces.
[0017] According to another preferred embodiment of the present
invention, the pair of clamp surfaces preferably include a
plurality of recesses arranged to hold the powder.
[0018] According to another preferred embodiment of the present
invention, the friction layers preferably include a material made
of a mixture of a binder and carbon black powder.
[0019] According to another preferred embodiment of the present
invention, the powder preferably has such a characteristic that,
when the belt is clamped between the pair of clamp surfaces, the
powder is not fused by heat that is generated by friction between
the belt and the pair of clamp surfaces.
[0020] According to another preferred embodiment of the present
invention, the powder preferably has a hardness that is less than
that of the pair of clamp surfaces.
[0021] Other elements, features, steps, characteristics and
advantages of the present invention will become more apparent from
the following detailed description of the preferred embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a side view of a motorcycle according to a first
preferred embodiment of the present invention that is mounted with
a belt-type continuously variable transmission.
[0023] FIG. 2 is a side view of a power unit according to the first
preferred embodiment of the present invention that includes a
four-cycle engine and the belt-type continuously variable
transmission.
[0024] FIG. 3 is a sectional view of the belt-type continuously
variable transmission according to the first preferred embodiment
of the present invention.
[0025] FIG. 4 is a side view of a belt used in the belt-type
continuously variable transmission according to the first preferred
embodiment of the present invention.
[0026] FIG. 5 is a sectional view of the belt used in the belt-type
continuously variable transmission according to the first preferred
embodiment of the present invention.
[0027] FIG. 6 is a sectional view along line F6-F6 in FIG. 5.
[0028] FIG. 7 is a sectional view schematically showing a state in
which a friction layer is stacked on a clamp surface of a primary
sheave in the first preferred embodiment of the present
invention.
[0029] FIG. 8 is a sectional view schematically showing a state in
which infusible powder is held on the clamp surface of the primary
sheave.
[0030] FIG. 9 is a sectional view schematically showing a state in
which infusible powder is interposed between the clamp surface of
the primary sheave and a contact surface of the belt.
[0031] FIG. 10 is a sectional view showing part A in FIG. 8 in an
enlarged scale.
[0032] FIG. 11 is a sectional view schematically showing a state in
which infusible powder is held on the contact surface of the belt
in the first preferred embodiment of the present invention.
[0033] FIG. 12 is a characteristic chart showing transition of
transmission torque of the belt with respect to driving time in the
first preferred embodiment of the present invention.
[0034] FIG. 13 is a side view of a belt-type continuously variable
transmission according to a second preferred embodiment of the
present invention showing a positional relationship between a high
friction portion of a sheave and a belt at the time when a
transmission gear ratio is maximum.
[0035] FIG. 14 is a side view of the belt-type continuously
variable transmission according to the second preferred embodiment
of the present invention showing a positional relationship between
the high friction portion of the sheave and the belt at the time
when a transmission gear ratio is minimum.
[0036] FIG. 15 is a side view of a primary sheave according to a
third preferred embodiment of the present invention.
[0037] FIG. 16 is a sectional view of the primary sheave according
to the third preferred embodiment of the present invention.
[0038] FIG. 17 is a sectional view of a belt according to a fourth
preferred embodiment of the present invention.
[0039] FIG. 18 is a characteristic chart showing a relationship
between thrust and transmission torque acting on a belt in a
conventional belt-type continuously variable transmission.
[0040] FIG. 19 is a characteristic chart showing a relationship
between thrust acting on the belt and an amount of heat generation
and transmission efficiency of the belt in the conventional
belt-type continuously variable transmission.
[0041] FIG. 20 is a characteristic chart showing transition of
transmission torque of the belt with respect to driving time in the
conventional belt-type continuously variable transmission.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0042] A first preferred embodiment of the present invention will
be hereinafter explained with reference to FIGS. 1 to 12.
[0043] FIG. 1 discloses a motorcycle 1 that is an example of a
vehicle according to a preferred embodiment of the present
invention. The motorcycle 1 has a frame 2. The frame 2 includes a
steering head pipe 3, a pair of main pipes 4 (only one main pipe 4
is shown) and a pair of seat rails 5 (only one seat rail 5 is
shown). The steering head pipe 3 is located at a front end of the
frame 2 and supports a front wheel 7 via a front fork 6.
[0044] Each of the main pipes 4 extends rearwards from the steering
head pipe 3. The main pipe 4 includes a front-half portion 4a that
extends obliquely downward from the steering head pipe 3, a
rear-half portion 4b that extends obliquely upward from a lower end
of the front-half portion 4a, and an intermediate portion 4c that
is located between the front-half portion 4a and the rear-half
portion 4b.
[0045] The seat rail 5 is suspended between the front-half portion
4a and the rear-half portion 4b of the main pipe 4. The seat rail 5
supports a seat 8 over which a rider straddles. The frame 2 is
covered with a body cover 9. The body cover 9 continues to the
lower end of the seat 8.
[0046] A rear arm bracket 10 is fixed to the intermediate portion
4c of each of the main pipes 4. The rear arm bracket 10 projects
downward from the intermediate portion 4c of the main pipe 4. The
rear arm bracket 10 supports a rear arm 11 that extends rearward.
The rear arm 11 is vertically swingable relative to the frame 2. A
rear end of the rear arm 11 supports a rear wheel 12 as a running
body.
[0047] The frame 2 supports a power unit 13 that drives the rear
wheel 12. As shown in FIGS. 1 and 2, the power unit 13 includes a
four-cycle single-cylinder engine 14 as a drive source and a
belt-type continuously variable transmission 15. This power unit 13
is covered with a lower part of the body cover 9.
[0048] The engine 14 is suspended at the front-half portion 4a of
the main pipe 4. The engine 14 includes a crank case 16 and a
cylinder 17 coupled to the crank case 16.
[0049] The crank case 16 contains a crank shaft 18 and a not shown
gear reduction unit. As shown in FIG. 3, the crank shaft 18 is
supported by the crank case 16 via bearings 19a and 19b. The crank
shaft 18 is horizontally arranged in a width direction of the
motorcycle 1.
[0050] The gear reduction unit has a drive sprocket 20 (shown in
FIG. 1) at an output end thereof. The drive sprocket 20 is located
behind the crank shaft 18. A chain 22 is wound between the drive
sprocket 20 and a driven sprocket 21 of the rear wheel 12.
[0051] The cylinder 17 of the engine 14 projects upward from the
crank case 16 along the front-half portion 4a of the main pipe 4.
The cylinder 17 contains a piston 23. The piston 23 is coupled to
crank webs 25a and 25b of the crank shaft 18 via a connecting rod
24.
[0052] As shown in FIGS. 2 and 3, the belt-type continuously
variable transmission (hereinafter referred to as "CVT") 15 is
located on the right side of the crank case 16. The CVT 15 is
contained in a transmission case 28. The transmission case 28 is
fixed to the right side surface of the crank case 16.
[0053] The CVT 15 includes a primary sheave 29, a secondary sheave
30, and a belt 31. The primary sheave 29 is located at a front end
of the transmission case 28 and supported by an input shaft 32. The
input shaft 32 is integrated with the crank shaft 18. In other
words, a journal section 18a located at the right end of the crank
shaft 18 is extended toward the front end of the transmission case
28 and this extended part also serves as the input shaft 32.
[0054] The primary sheave 29 includes a fixed plate 34a and a
sliding plate 34b. The fixed plate 34a is fixed to a shaft end of
the input shaft 32 and rotates together with the input shaft 32.
The sliding plate 34b has a cylindrical boss portion 35. The boss
portion 35 is supported on the input shaft 32 via a collar 36.
Thus, the sliding plate 34b is slidable in directions the sliding
plate 34b approaches and moves away from the fixed plate 34a. The
sliding plate 34b is rotatable in a peripheral direction of the
input shaft 32.
[0055] The primary sheave 29 has a pair of first clamp surfaces 37a
and 37b. One first clamp surface 37a is formed on the fixed plate
34a. The other first clamp surface 37b is formed on the sliding
plate 34b. The first clamp surfaces 37a and 37b have a conical
shape and are opposed to each other. The first clamp surfaces 37a
and 37b define a first belt groove 38 having a V-sectional shape
between the fixed plate 34a and the sliding plate 34b. Width L1 of
the first belt groove 38 is adjusted by sliding movement of the
sliding plate 34b.
[0056] A cam plate 39 is fixed to an outer periphery of the input
shaft 32. The cam plate 39 rotates together with the input shaft 32
and is opposed to the sliding plate 34b. The sliding plate 34b is
hooked on the cam plate 39 so as to be slidable in the axial
direction of the input shaft 32. Accordingly, the cam plate 39 and
the sliding plate 34b are movable in directions in which the cam
plate 39 and the sliding plate 34b approach and move away from each
other while rotating together.
[0057] The sliding plate 34b has a cam surface 40 that is opposed
to the cam plate 39. Plural roller weights 41 (only one roller
weight is shown) are interposed between the cam surface 40 and the
cam plate 39. The roller weight 41 moves along the cam surface 40
with centrifugal force that is generated when the crank shaft 18
rotates. According to the movement, the sliding plate 34b slides in
the axial direction of the input shaft 32 and the width L1 of the
first belt groove 38 changes.
[0058] The secondary sheave 30 is located at a rear end of the
transmission case 28 and is supported on an output shaft 42. The
output shaft 42 is arranged in parallel to the input shaft 32 and
coupled to an input end of the gear reduction unit via a not shown
automatic centrifugal clutch.
[0059] The secondary sheave 30 includes a fixed plate 45a and a
sliding plate 45b. The fixed plate 45a has a cylindrical collar 46
at a rotational center thereof. The collar 46 meshes with the outer
peripheral surface of the output shaft 42. According to this
meshing, the fixed plate 45a and the output shaft 42 rotate
together.
[0060] The sliding plate 45b has a sleeve 47 at a rotational center
thereof. The sleeve 47 is provided on the outer peripheral surface
of the collar 46 so as to be slidable in the axial direction.
Plural engagement grooves 48 are formed in the sleeve 47. The
engagement grooves 48 extend in the axial direction of the sleeve
47 and are arranged in the peripheral direction of the sleeve 47 at
intervals.
[0061] The collar 46 has plural engaging pins 49. The engaging pins
49 project to the outside of the collar 46 and are slidably fitted
in the engagement grooves 48 of the sleeve 47. Consequently, the
fixed plate 45a and the sliding plate 45b are movable in directions
in which the fixed plate 45a and the sliding plate 45b approach and
move away from each other while rotating together.
[0062] The secondary sheave 30 has a pair of second clamp surfaces
51a and 51b. One second clamp surface 51a is formed on the fixed
plate 45a. The other second clamp surface 51b is formed on the
sliding plate 45b. The second clamp surfaces 51a and 51b are formed
in a conical shape and are opposed to each other. The second clamp
surfaces 51a and 51b define a second belt groove 52 having a
V-sectional shape between the fixed plate 45a and the sliding plate
45b. Width L2 of the second belt groove 52 is adjustable according
to sliding movement of the sliding plate 45b.
[0063] A spring seat 53 is secured to an end of the collar 46. The
spring seat 53 is opposed to the sliding plate 45b. A compression
coil spring 54 is interposed between the spring seat 53 and the
sliding plate 45b. The spring 54 biases the sliding plate 45b
toward the fixed plate 45a.
[0064] As shown in FIG. 3, the belt 31 is endlessly wound between
the first belt groove 38 of the primary sheave 29 and the second
belt groove 52 of the secondary sheave 30. As shown in FIGS. 4 to
6, the belt 31 includes a plurality of resin blocks 56 and a pair
of coupling members 57.
[0065] Polyamide resin is used for the resin blocks 56 as a matrix.
Carbon fibers or aramid fibers are mixed in the matrix as
reinforcement material. The polyamide resin has a high heat
resistance and is resistive to a repeated impact load. The
polyamide resin can maintain a stable quality over a long time
period. The carbon fibers and aramid fibers have both high strength
and heat resistance. Therefore, the resin blocks 56 are excellent
in heat resistance, wear resistance, and fatigue resistance.
[0066] As shown in FIG. 5, each of the resin blocks 56 has a pair
of contact surfaces 58a and 58b. The contact surfaces 58a and 58b
are located apart from each other in the width direction of the
belt 31. The contact surfaces 58a and 58b are inclined so as to
extend along the first clamp surfaces 37a and 37b of the primary
sheave 29 and the second clamp surfaces 51a and 51b of the
secondary sheave 30, respectively. Recesses 59 are formed in
central parts of the contact surfaces 58a and 58b of each of the
resin blocks 56 respectively.
[0067] The coupling members 57 are formed of, for example,
refractory rubber. Plural core wires 60 for reinforcement are
buried in the coupling members 57. The coupling members 57 have an
annular shape and are fitted in the recesses 59 of the resin block
56. Through this fitting, the resin blocks 56 are coupled to one
another to constitute the endless belt 31.
[0068] The coupling member 57 fitted in the recesses 59 retracts
from the contact surfaces 58a and 58b of the resin blocks 56.
Therefore, when the belt 31 is wound around the first and the
second belt grooves 38 and 52, only the contact surfaces 58a and
58b of the resin blocks 56 come into contact with the first clamp
surfaces 37a and 37b of the primary sheave 29 and the second clamp
surfaces 51a and 51b of the secondary sheave 30.
[0069] In other words, the first clamp surfaces 37a and 37b of the
primary sheave 29 and the second clamp surfaces 51a and 51b of the
secondary sheave 30 clamp the resin blocks 56 of the belt 31 with
predetermined thrust. Consequently, desired transmission torque is
obtained between the primary sheave 29 and the belt 31 and between
the secondary sheave 30 and the belt 31.
[0070] In a state in which the rotation speed of the crank shaft 18
is low, for example, at the time the engine 14 is idling, the
roller weights 41 are shifted to a rotational center of the primary
sheave 29. Therefore, the sliding plate 34b is located in a
position farthest from the fixed plate 34a and the width L1 of the
first belt groove 38 is maximized. Consequently, the belt 31 wound
around the first belt groove 38 is located at the rotational center
of the primary sheave 29. A diameter of the belt 31 wound around
the primary sheave 29 is minimized.
[0071] On the other hand, in the secondary sheave 30, the sliding
plate 45b is biased toward the fixed plate 45a by the spring 54.
The width L2 of the second belt groove 52 is minimized.
Consequently, the belt 31 wound around the second belt groove 52 is
pushed out to an outer periphery of the secondary sheave 30. A
diameter of the belt 31 wound around the secondary sheave 30 is
maximized. Therefore, the CVT 15 has a maximum transmission gear
ratio.
[0072] As the number of revolutions of the crank shaft 18
increases, the roller weights 41 move outward in a radial direction
of the sliding plate 34b with the centrifugal force. According to
this movement, the sliding plate 34b slides toward the fixed plate
34a and the width L1 of the first belt groove 38 gradually
decreases. As a result, the belt 31 clamped between the first clamp
surfaces 37a and 37b is pushed outward in a radial direction of the
primary sheave 29. A diameter of the belt 31 wound around the
primary sheave 29 increases.
[0073] Conversely, in the secondary sheave 30, the belt 31 is
pulled toward the rotational center of the secondary sheave 30.
Consequently, the sliding plate 45b slides in a direction in which
the sliding plate 45b moves away from the fixed plate 45a against
the biasing force of the spring 54. The width L2 of the second belt
groove 38 gradually increases. Therefore, a diameter of the belt 31
wound around the secondary sheave 30 decreases. Thus, the
transmission gear ratio of the CVT 15 decreases. The transmission
gear ratio of the CVT 15 is minimized when a diameter of the belt
31 wound around the primary sheave 29 is maximized.
[0074] The fixed plate 34a of the primary sheave 29 and the fixed
plate 45a of the secondary sheave 30 are formed of, for example,
chromium-molybdenum steel (SCM420) subjected to carburizing,
quenching, and tempering treatment. The fixed plates 34a and 45a
have surface hardness indicated by 80.+-.2 HRA. The sliding plate
34b of the primary sheave 29 is formed of a die-cast aluminum alloy
(YDC11) subjected to surface treatment such as chrome plating. The
sliding plate 34b has surface hardness indicated by 800 HV or more.
The sliding plate 45b of the secondary sheave 30 is formed of
mechanical structure carbon steel (S35C) and has surface hardness
indicated by 63 HB.
[0075] The first clamp surfaces 37a and 37b of the primary sheave
29 and the second clamp surfaces 51a and 51b of the secondary
sheave 30 are finished in a predetermined shape by machining such
as cutting or grinding. Consequently, as represented by the first
clamp surface 37a of the primary sheave 29 in FIG. 7, the first
clamp surface 37a has a large number of grooves 62 formed by
machining. The grooves 62 are very fine with width and depth of
about several .mu.m. The grooves 62 are a kind of recess.
[0076] The first clamp surfaces 37a and 37b of the primary sheave
29 and each of the second clamp surfaces 51a and 51b of the
secondary sheave 30 are covered with friction layers 63 entirely,
respectively. The friction layers 63 are obtained by coating, for
example, carbon powder 64, which is a friction enhancing material,
on the first clamp surfaces 37a and 37b and the second clamp
surfaces 51a and 51b, for which machining has been completed. As
represented by the first clamping surface 37a of the primary sheave
29 in FIG. 7, the friction layer 63 is stacked on the first clamp
surface 37a so as to have thickness enough for burying the grooves
62 sufficiently.
[0077] The friction layers 63 do not always have to cover the
entire first and second clamp surfaces 37a, 37b, 51a, and 51b. For
example, in the first and the second clamp surfaces 37a, 37b, 51a,
and 51b, only regions in contact with the belt 31 may be covered
with the friction layers 63. In addition, in the first and the
second clamp surfaces 37a, 37b, 51a, and 51b, only regions, which
clamp the belt 31 when the CVT 15 has a maximum transmission gear
ratio, may be covered with the friction layers 63.
[0078] The carbon powder 64 has infusibility. The carbon powder 64
has such a characteristic as to withstand the heat and pressure
that are generated during the speed change operation of the CVT 15.
More specifically, when the belt 31 is clamped between the first
clamp surfaces 37a and 37b of the primary sheave 29 and between the
second clamp surfaces 51a and 51b of the secondary sheave 30, heat
due to friction is generated in contact parts between the contact
surfaces 58a and 58b of the belt 31 and the first and the second
clamp surfaces 37a, 37b, 51a, and 51b. Consequently, since the
carbon powder 31 has such a characteristic that carbon powder is
not fused by the heat in the contact parts, the carbon powder 31
can maintain the powder state.
[0079] In addition, the carbon powder 64 has hardness lower than
that of the first clamp surfaces 37a and 37b of the primary sheave
29 and the second clamp surfaces 51a and 51b of the secondary
sheave 30.
[0080] In the new CVT 15 that has just been assembled, the first
clamp surfaces 37a and 37b of the primary sheave 29 and the second
clamp surfaces 51a and 51b of the secondary sheave 30 are covered
with the friction layers 63. Consequently, the carbon powder 64 is
in a state in which the carbon powder 64 is held on the first and
the second clamp surfaces 37a, 37b, 51a, and 51b.
[0081] If the driving of the new CVT 15 is started, as represented
by the primary sheave 29 in FIG. 9, the carbon powder 64 enters a
slight gap g between the primary sheave 29 and the belt 31 at the
initial stage of driving. Consequently, a contact area of the
primary sheave 29 and the belt 31 and a contact area of the
secondary shave 30 and the belt 31 increase. The carbon powder 64
has infusibility in that the carbon powder 64 maintains the powder
state even if heat is applied during the speed change operation.
Therefore, the carbon powder 64 functions as a slip-stopper for the
belt 31.
[0082] FIGS. 8 and 10 disclose a state of the first clamp surface
37a at the time when the driving of the CVT 15 is continues. Since
the other first clamp surface 37b and the second clamp surfaces 51a
and 51b have the same state as that of the first clamp surface 37a,
the first clamp surfaces 37a is described here as a
representative.
[0083] As driving time elapses, a part of the friction layer 63
covering the first clamp surface 37a is removed from the first
clamp surface 37a by the contact with the belt 31 and dispersed
into the transmission case 28. Consequently, the carbon powder 64,
which enters into the grooves 62, remains on the first clamp
surface 37a. At the same time, edges of the grooves 62 are scraped
off by the contact with the belt 31, resulting in a decrease in
depth of the grooves 62.
[0084] On the other hand, in the belt 31, the contact surfaces 58a
and 58b of resin blocks 56 are scraped off by the contact with the
first clamp surface 37a. Consequently, initial wear of the belt 31
occurs. As shown in FIG. 10, a scraped resin component 65 of the
belt 31 is transferred to the groove 62 and cooperates with the
carbon powder 64 to fill the groove 62. The first clamp surface 37a
is smoothed.
[0085] As shown in FIG. 11, the carbon powder 64 adheres to the
contact surface 58a of the resin block 56. The carbon powder 64
fills uneven portions on the contact surface 58a, thereby smoothing
the contact surface 58a. Therefore, the contact state between the
contact surface 58a of the belt 31 and the first clamp surface 37a
of the primary sheave 29 is stabilized.
[0086] According to such a first preferred embodiment of the
present invention, at the initial stage of driving of the CVT 15,
the carbon powder 64 prevents slipping of the belt 31.
Consequently, without increasing thrust for clamping the belt 31,
it is possible to improve torque transmission efficiency between
the primary sheave 29 and the belt 31 and between the secondary
sheave 30 and the belt 31 at the beginning of driving. This makes
trial-run unnecessary.
[0087] After fixed time elapses from the beginning of driving, the
friction layer 63 is removed and the residual carbon powder 64
fills the grooves 62 of the first clamp surface 37a. Consequently,
the slip prevention function of the carbon powder 64 is lost. The
transmission torque changes to a value corresponding to the thrust
between the primary sheave 29 and the belt 31 and between the
secondary sheave 30 and the belt 31.
[0088] FIG. 12 discloses transition of transmission torque
following elapse of driving time at the initial stage of driving in
CVT 15 of this preferred embodiment. As shown in FIG. 12, a value
of transmission torque A at the initial stage of driving is
slightly higher than a predetermined original value of transmission
torque B because of the presence of the carbon powder 64. This
value of the transmission torque A gradually decreases as time
elapses and finally coincides with a value of normal transmission
torque B. The reason appears to be that the friction layer 63 is
removed by the contact with the belt 31 and the slip prevention
function of the carbon powder 64 at the initial stage of driving is
lost.
[0089] According to the above-described structure, the carbon
powder 64 has hardness lower than that of the first clamp surfaces
37a and 37b of the primary sheave 29 and the second clamp surfaces
51a and 51b of the secondary sheave 30. Consequently, the carbon
powder 64 never damages the first clamp surfaces 37a and 37b or the
second clamp surfaces 51a and 51b. Therefore, it is possible to
control wear of the first clamp surfaces 37a and 37b or the second
clamp surfaces 51a and 51b.
[0090] Moreover, according to this preferred embodiment, the plural
resin blocks 56 constituting the belt 31 are formed of polyamide
resin. Thus, the heat resistance and durability of the belt 31 are
improved and stable performance of the belt 31 can be maintained
over a long time period.
[0091] FIGS. 13 and 14 disclose a second preferred embodiment of
the present invention. The second preferred embodiment differs from
the first preferred embodiment in the first clamp surfaces 37a and
37b of the primary sheave 29 and the second clamp surfaces 51a and
51b of the secondary sheave 30. The other components of the CVT 15
in the second preferred embodiment are the same as those in the
first preferred embodiment. Consequently, in the second preferred
embodiment, the components same as those in the first preferred
embodiment are denoted by like reference numerals and explanations
of the components are omitted.
[0092] The first clamp surfaces 37a and 37b of the primary sheave
29 have high friction portions 71. Similarly, the second clamp
surfaces 51a and 51b of the secondary sheave 30 have high friction
portions 72. The high friction portions 71 and 72 are obtained by
subjecting the first clamp surfaces 37a and 37b and the second
clamp surfaces 51a and 51b to shot peening or honing respectively.
The high friction portions 71 and 72 include a large number of fine
uneven portions. The uneven portions are formed to have a net-like
pattern with no orientation.
[0093] The high friction portions 71 of the primary sheave 29 are
annularly formed at the rotational center of the first clamp
surfaces 37a and 37b. Consequently, when a diameter of the belt 31
wound around the primary sheave 29 is minimized, the belt 31 is
clamped between the high friction portions 71. Portions of the
first clamp surfaces 37a and 37b out of the high friction portions
71 are machined surface portions 73 subjected to machining such as
cutting or grinding. The high friction portions 70 have a friction
coefficient higher than that of the machined surface portion
73.
[0094] The high friction portions 72 of the secondary sheave 30 are
annularly formed at the outer periphery of the second clamp
surfaces 51a and 51b. Consequently, when a diameter of the belt 31
wound around the secondary sheave 30 is maximized, the belt 31 is
clamped between the high friction portions 72. Portions of the
second clamp surfaces 51a and 51b out of the high friction portions
72 are machined surface portions 74 subjected to machining such as
cutting or grinding. The high friction portions 72 have a friction
coefficient higher than that of the machined surface portions
74.
[0095] Although not shown, the first clamp surfaces 37a and 37b and
the second clamp surfaces 51a and 51b are covered with the same
friction layers as in the first preferred embodiment. The friction
layers are stacked on the first clamp surfaces 37a and 37b and the
second clamp surfaces 51a and 51b to thickness enough for filling
the grooves formed by machining and the uneven portions of the high
friction portions 71 and 72.
[0096] According to such a structure, the belt 31 is clamped
between the high friction portions 71 of the primary sheave 29 and
the high friction portions 72 of the secondary sheave 30 in such a
driving state that a diameter of the belt 31 wound around the
primary sheave 29 is minimized and a diameter of the belt 31 wound
around the secondary sheave 30 is maximized. In other words, in
such a driving state that the transmission gear ratio of the CVT 15
is maximized, the belt 31 is clamped between portions of the first
clamp surfaces 37a and 37b and the second clamp surfaces 51a and
51b having high friction coefficients.
[0097] Consequently, at the initial stage of driving, the carbon
powder 64 tends to stop between the primary sheave 29 and the belt
31 and between the secondary sheave 30 and the belt 31. Thus,
slipping of the belt 31 can be surely prevented in such a driving
state that the transmission gear ratio of the CVT 15 is maximized
and the tension acting on the belt 31 is maximized.
[0098] According to the structure described above, as the
transmission gear ratio of the CVT 15 gradually decreases, the belt
31 moves out of the high friction portions 71 and 72. Therefore, it
is possible to prevent wear of the belt 31 in such a driving state
that the tension acting on the belt 31 decreases.
[0099] The high friction portions 71 and 72 only have to be formed
on a part of the first clamp surfaces 37a and 37b and the second
clamp surfaces 51a and 51b. A range of machining for obtaining the
high friction portions 71 and 72 is small. Accordingly,
manufacturing cost of the primary sheave 29 and the secondary
sheave 30 can be reduced.
[0100] FIGS. 15 and 16 disclose a third preferred embodiment of the
present invention.
[0101] In the third preferred embodiment, the fixed plate 34a of
the primary sheave 29 is described as an example. As shown in FIG.
15, plural rib-like projections 81 are formed on the first clamp
surface 37a of the fixed plate 34a. The projections 81 extend
radially from the rotational center of the fixed plate 34a over the
entire first clamp surface 37a. The projections 81 define plural
radial grooves 82 over the first clamp surface 37a. The projections
81 and the grooves 82 are alternately arranged on the first clamp
surface 37a. Consequently, the entire first clamp surface 37a
functions as a high friction portion 83 with a high friction
coefficient.
[0102] Although not shown, the first clamp surface 37a is coated
with the same friction layer as in the first preferred embodiment.
The friction layer is stacked on the first clamp surface 37a to
thickness sufficient for filling the projections 81 and the grooves
82.
[0103] According to this structure, since the high friction portion
83 is located over the entire first clamp surface 37a, the carbon
powder is surely held on the first clamp surface 37a. Even if the
position of the wound belt 31 changes, slipping of the belt 31 can
be prevented.
[0104] FIG. 17 discloses a fourth preferred embodiment of the
present invention.
[0105] In the fourth preferred embodiment, the contact surfaces 58a
and 58b of the belt 31 are covered with friction layers 63 which
increases the friction. The structure of the belt 31 is the same as
that in the first preferred embodiment. In addition, as in the
first preferred embodiment, the friction layers 63 contain
infusible carbon powder.
[0106] According to the fourth preferred embodiment, the friction
layers 63 are stacked on the contact surfaces 58a and 58b of the
belt 31 to thickness sufficient for filling the uneven portions of
the contact surfaces 58a and 58b of the belt 31.
[0107] When the new belt 31 is wound between the primary sheave and
the secondary sheave, the friction layers 63 are interposed between
the belt 31 and both the sheaves. In the initial stage of driving,
the carbon powder contained in the friction layers 63 enters slight
gaps between the belt 31 and both the sheaves. Consequently,
contact areas between the belt 31 and the respective sheaves
increase. As a result, as in the first preferred embodiment, the
carbon powder functions as a slip-stopper for the belt 31.
[0108] In the first preferred embodiment, the carbon powder 64 is
used as a slip-stopper for the belt 31. However, the present
invention is not limited to this preferred embodiment. Other kinds
of powder such as carbon black may be used.
[0109] Specifically, graphite powder, which is a kind of carbon
black, is usable. It is preferable to use graphite powder with a
grain size of 5 .mu.m to 150 .mu.m. When graphite powder is used to
form a friction layer, first, a liquid-phase material obtained by
mixing graphite powder with a binder and a diluent is prepared. The
liquid-phase material is applied to at least one of a primary
sheave, a secondary sheave, and a belt.
[0110] The binder is resin for fixing the graphite powder to the
primary sheave, the secondary sheave, or the belt. As this resin,
acrylic resin or olefin resin is suitable taking into account
drying time and loadings of the liquid-phase material. The diluent
keeps viscosity of the liquid-phase material properly to make it
easy to adjust density and thickness of the friction layer and
improve work efficiency in applying the liquid-phase material.
Examples of the diluent include an ester solvent represented by
butyl acetate, a ketone solvent represented by methyl ethyl ketone,
a petroleum solvent represented by hexane, and an alcohol solvent
represented by methyl alcohol.
[0111] It is desirable that a compounding ratio of the graphite
powder, the binder, and the diluent is set to 2 to 80 wt % for the
graphite powder and the remaining 20 to 98 wt % for the binder and
the diluent.
[0112] It is possible to use powdery zinc oxide or particulate
silica powder for stopping the slipping of the belt 31. However,
the carbon powder is inexpensive compared with zinc oxide and is
advantageous in terms of cost. Besides, the carbon powder has low
hardness compared with silica and does not easily damage the
sheave. Thus, taking into account cost and an effect on sheaves, it
is desirable to use the carbon powder.
[0113] In the first preferred embodiment, friction layers are
formed on both the primary sheave and the secondary sheave.
However, the present invention is not limited to this. Friction
layers may be formed on one of the primary sheave and the secondary
sheave. According to this constitution, powder contained in the
friction layers is fed to the other sheave, which has no friction
layer, via the belt. Therefore, it is possible to prevent slipping
between both the sheaves and the belt.
[0114] When the present invention is carried out, friction layers
may be formed on all of the primary sheave, the secondary sheave,
and the belt.
[0115] The vehicle according to the present invention is not
limited to a motorcycle. The present invention is similarly
applicable to, for example, an ATV (All-Terrain Vehicle) with three
or four wheels for running on rough grounds or to a snowmobile.
[0116] According to various preferred embodiments of the present
invention, the infusible powder prevents slipping of the belt at
the initial stage of driving. Consequently, without increasing the
thrust for clamping the belt, the torque transmission efficiency
can be improved between the primary sheave and the belt and between
the secondary sheave and the belt. Therefore, a desired
transmission torque can be obtained from the beginning of driving
and trial-run is made unnecessary.
[0117] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing the scope and spirit of the present invention. The scope
of the present invention, therefore, is to be determined solely by
the following claims.
* * * * *